Colored pigment for camouflage coating compositions



62. 05 8d o8 m W. M. FOSS Filed March-6. 1955 June 18, 1957 COLOREDPIGuEN'r FOR CAMOUFLAGE COATING COMPOSITIONS INVENTOR Warren M. Foss MJW ' AGENT aouppauag aouougwsum IUGOJBd COLORED PIGMENT FOR CAMOUFLAGECOATING COMPOSITIONS Warren M. Foss, Nixon, N. 'J., assignor to NationalLead Company, New York, N. Y., a corporation of New Jersey 7 ApplicationMarch 6, 1953, Serial No. 340,880

1 Claim. (Cl. 106-300) The present invention relates in general topigment materials and more particularly to a colored pigment for use inpreparing camouflage coating compositions such as paints, varnishes andthe like, the present application being a continuation in part of the'copending application of Foss et al., Serial No. 308,662, filedSeptember 9, 1952, for an improved colored pigment and method for makingsame. 7

Earlier work in the field of camouflage paints has established what arenow regarded as the primary requisites of a camouflage coatingcomposition, namely that it have a visually dark green color akin tothat of natural foliage and that it possess the high infra redreflectancevalue of naturalfoliage or more particularly chlorophyllwhich characterizes the infra red reflectance value of natural greenfoliage.

It has been noted that the spectrophotometric curve of chlorophyll has acharacteristically sharp rise in reflectance value in the relativelyshort wave length range of from about 670 to about 750 millimicrons andthat inasmuch as camouflage paints heretofore used have not has theeifect of increasing the reflectance values of these pigmentcompositions and in particular the slope of the spectrophotometriccurves in that critical region of thewavelength band which lies betweenabout 670 and 750 millimicrons. v

An object of the present invention is to provide a superior greenpigment which is economical to manufacture and which when used in apaint vehicle will form camouflage coating compositions having highhiding power.

Another object of the invention is to provide a superior green pigmenthaving spectrophotometric characteristics substantially similar tochlorophyll. Y

.A further object of the invention is to provide a superior camouflagecoating composition having a dark green color akin to natural foliageand a sharp rise in percent reflect ance value in the critical region ofthe wave length hand between about 670and 75.0 millimicrons.

These and other objects become apparent from the following more.complete description of the invention.

. In its broadest aspect the present invention relates to the formationof a green pigment comprising a chemical and/ or physical combination ofantimony oxide with the oxidic compounds of chromium, cobaltandtitaniuin in such proportions that the spectrophotometriccurve of.the green pigment has a sharp rise in reflectance value bepigmentstowardslonger wave lengths.

reflectance value of a paint is lowered when applied to Patented June18, 1957 tween about 670 to about 750 millimicrons correspond ingsubstantially to that of chlorophyll; and which when mixed with a paintvehicle will provide a camouflage coating composition having high hidingpower and good resistance to weathering. I

With respect to the use hereinafter of the phrase green pigment, it willbe understood that the latter is used collectively to designate theplurality of green pigments which are included within the purview of theinvention and which, as illustrated herein and hereinafter described,may be represented graphically by. a family of spectrophotometric curveshaving the sharp rise in percent reflect-' ance value within thecritical wave length range of about 670 to 750 millimicrons whichcharacterizes the spectrophotometric curve of chlorophyll.

In general the camouflage coating compositions disclosed in theabove-identified'copending application of Foss et a1. were formed fromintimate mixtures of chromium sesquioxide, having the formula CrzOs, andsometimes referred to hereinafter as chromium oxide; 00- baltous oxide;and titanium dioxide, the oxides of chromium, cobalt and titanium beingpreferably in the form of chromium sesquioxide, cobalt carbonate and aneutralized hydroustitanium oxide such as obtained by hydrolysis oftitanium salt solutions, for example titanium sulfate solutions; andthereafter calcining the mixture at a temperature of about 900 C. to1000 C. for a period of from /2 hour to 2 hours. The calcination of themixture results in a chemical'and/ or physical combination of theconstituents to form a green pigment which upon X-ray and microscopicanalysis appears to comprise mixed crystals of cobalt chromite, cobaltorthotitanate and titanium dioxide.

While the latter are probably the actual chemical compounds in thepigment, it has been found to serve the purpose of the descriptionbetter to refer to these chemical compounds percentagewise in terms ofthe percent by weight of the chromium oxide, cobaltous oxide andtitanium dioxide contained in-the green pigment.

The relative amounts of the oxidic compounds used to form a coloredpigment vary over a considerable range. It was found that when thenumber of mol parts of cobaltous oxide was equal to or less than Sthenumber of mol parts of chromium oxide, then for a constant amount oftitanium dioxide such as, for example 5v mols, the range of mols ofcobaltous oxide and chromium oxide may vary from 0.2 to 5 mols; and thatwhen the amount of cobaltous oxide exceeds the amount of chromium oxide:(a) the mol ratio of cobaltous oxide and chromium oxide must be 5 orless and (b) the range of chromium oxide may be from 0.2 to 4.9 mols andthe range of cobaltous oxide may be from 0.21 to 5 mols for each 5 molsof titanium dioxide.

As pointed out below, the latter ratio of oxidic compounds is notapplicable to thepresent invention and hence, whenever reference is madehereinafter to chromium-cobaltous-titanium oxide systems, it will beunderstood that only those systems are included wherein the number ofmol parts of cobaltous oxide are equal to or less than the number of molparts of chromium oxide.

In general, the addition of an oxide of antimony to thecobaltous-chromium-titanium dioxide system has been found not only toincrease the visible and infra-red reflectance values of these greenpigments but also to shift the green peaks of the spectrophotometriccurves of these Normally the dark surfaces such as,'for example blackmetal surfaces, dark wood-s, etc. and consequently an increase in thevisible range and in the infra red range is advantageous.

However, more important than these advantages, by far, is the fact thatthe addition of the oxides of antimony increases the slope of thespectrophotometric curve of pigment compositions of thecobaltous-chromium-titanium dioxide system in the critical wave lengthregion of from 670 to 750 millimicrons so that the spectrophotometriccurves of these pigments correspond substantially exactly to the slopeof the chlorophyll curve in the corresponding region of the wave lengthband.

More particularly, it has been found that the sharp increase in slope ofthe spectrophotometric curves of cobaltous-chromium-titaniurn dioxidesystems within the above-identified critical wave length range occursonly when an oxide of antimony is added to systems comprisingsubstantially equimolar amounts of cobaltous oxide and chromium oxidewith anexcess of titanium dioxide; and to systems containing an excessof chromium oxide and titanium dioxide over the cobaltous oxide.However, for systems wherein the cobaltous oxide is in excess of thechromium oxide, the addition of an oxide of antimony has substantiallyno effect on the critical slope of the spectrophotometric curve of thecobaltous, chromium oxide, titanium dioxide series of compositions.

Further, it has been discovered that in both of these systems i. e.wherein the cobaltous oxide and chromium oxide are in equimolar ratios,and in a system wherein the chromium oxide exceeds the amount ofcobaltous oxide, the amount of antimony oxide to be added to thesesystems bears a direct relationship to the molar amount of cobaltousoxide in the system.

Specifically, experimental work has shown that incobaltous-chromium-titanium dioxide systems having equimolar amounts ofcobaltous oxide and chromium oxide ranging from 0.5 to 5 mols per 5 molsof titanium dioxide, the maximum amount of antimony oxide which may betolerated in these systems is substantially 0.5 the molar amount ofcobaltous oxide present in any particular one of these systems; and thatfor systems involving an excess of chromium oxide over the cobaltousoxide the maximum additions of antimony oxide may range as high as about0.9 the molar amount of cobaltous oxide present in any particular one ofthese systems. Moreover, for both types of systems, that is to say forequimolar amounts of cobaltous oxide and chromium, and for systemswherein the chromium oxide is in excess ofthe cobaltous oxide, theaddition of about 0.1 mol part of antimony trioxide has been found to bethe minimum amount required to secure appreciable increases in thereflectance value of these systems and in particular a relatively sharpincrease in the-slope of their spectrophotometric curves in the criticalwave length region of from 670 to 750 millimicrons.

The following table illustrates, on a mol basis, effective amounts ofantimony oxide, as antimony trioxide, to be added to variouscobaltous-chrornium-titanium dioxide systems for achieving the sharprise in reflectance value which characterizes that of chlorophyll in theaboveidentified critical wave length region.

TABLE I OrzOa 000 l T102 SbaOa 0. 5 0. 5 5 0. 1-0. 25 1. 1. 0 0. 1-0. 53. o 3. 0 5 0. 1-1. 5 5. 0 5. 0 5 0. 1-2. 5 1. 0 u. 5 5 0. 1-0. 45 3.0 1. 0 5 0. 1-0. 9 5. o 3. 0 5 0. 1-2. 7

availability and cost considerations, it will be understood that otheroxidic compounds of chromium and cobalt may be used. For example, thesulfates, acetates, and chlorides of chromium and cobalt may be used incombination with antimony trioxide and the hydrate of titanium and infact any compounds of chromium, cobalt, antimony trioxide and titaniummay be used which, when heated during the calcination state, will give amolar composition comprising chromium oxide, cobaltous oxide, antimonytrioxide and titanium dioxide. Although antimony trioxide is preferredfrom the standpoint of economy and convenience, it will be understoodthat other oxides of antimony may be used such as antimony pentoxide.

With respect to the source of titanium dioxide, a hydrous titanium oxideprovides an aqueous medium which is idea-l for forming a slurry of theoxidic compounds of titanium chromium, antimony and cobalt. The hydratemay be treated with a neutralizing agent to prevent the formation ofcobalt sulfate and facilitate the easy removal of ammonium'sulfateduring calcination.

After the mixture of materials has been thoroughly agitated, the slurryis then partially dried and transferred directly to a continuous rotarykiln in which the first portion of the kiln will act as a drier and thesubsequent portion of the kiln as a calciner. The dried material iscalcined at a temperature of from about 900 C. to about 1000 C., theoptimum calcining temperature being about 1000 C.

The calcination time has no appreciable eflect upon the color of thepigment or its spectrophotometric curve other than to lower itsreflectance value slightly but should generally be between /2 to 2 hoursand preferably about 1 hour. Batches of dried material calcined underthese preferred conditions are dark green in appearance, are

soft and free from grit, and hence are ideally suited for incorporationinto paint vehicles for the formation of camouflage coatingcompositions.

For visualizing the spectrophotometric characteristics of green pigmentsmade by the process of this invention, reference may be made to Figure1, the shaded area of which is comprehensive of the spectrophotometriccurves of any one of the improved green pigments within the scope ofthis invention. Included with these curves, for comparison, is thespectrophotometric curve (H) of chlorophyll and the spectrophotometriccurve (0) of a pigment composition of the chromium-cobalt-titanium oxidesystem to which antimony trioxide has not been added. By way ofexplanation, it will be seen that the graph covers the range of wavelength from the lower end of the visible range (VR) corresponding toabout 450 millimicrons through a portion of the near infra-red range(IR) to a point corresponding to about 850 millimicrons, the upper endof the visual range coinciding with the lower end of the near infra-redrange at about 700 millimicrons.

Thechlorophyll curve (H) is characterized by a peak reflectance value,sometimes hereinafter referred to as the green peak (p) at about 550millimicrons, a minimum reflectance value of about 5% at about 670millimicrons and an extremely sharp rise in reflectance value of from 5to 51% within the critical range of from 670 millimicrons to about 750millimicrons.

The three curves a, b, and c in the shaded area of Figure 1 comprisepigment materials having the compositions listed below:

Orion O00 TiOz SbzOa Mols Mols Mols Male ((1) 3 3 5 1 b) 3 3 5 0. 5 3 35 As shown, the curves a and b, which are characteristic of the pigmentcompositions of this invention, start at the lower end of the visiblerange at percent reflectance values corresponding substantially to thatof chlorophyll and rise to green peaks at about 535 millimcrons withreflectance values ranging from about 18 to 19 percent which are abovethe percent reflectance value of chlorophyll at its green peak (p). Fromtheir green peaks the curves fall off rather sharply and aresubstantially parallel to but above the corresponding slope of thechlorophyll curve to a point opposite about 600 millimicrons from whichpoint the curves slope downwardly at substantially flat angles torelatively low reflectance values of from about 7% to about 8% at about670 millimicrons. From 670 to 750 millimicrons the curves rise sharplyin percent reflectance values. Curve a which is typical in the antimonytreated chromiumcobaltous titanium dioxide system of curves, has a lowreflectance value of about 8% and a high of about 46% which is anincrease of about 38 reflectance value units in the critical wave lengthrange of 670 to 750 millimicrons and compares favorably with an increaseof about 46 units in reflectance value of the chlorophyll curve in thissame wave length range. The curve b follows closely the curvature ofcurve a and has an increase of about 41 units in percent reflectancevalue in the critical wave length range of from 670 to 750 millimicrons.

Other compositions having a sharp rise in percent reflectance valuewithin the critical wave length range defined above are listed belowwherein AR represents the number of units increase in percentreflectance value within the range of 670 to 750 millimicrons.

OnO: COO T: Ebro: AR

Mala Mala Mala Mala M014 0. 5 0. 5 6 0. 1 35 0. 5 0. 5 5 0. 25 38 1 1 50. 1 40 1 1 5 0. 5 38 2 1 5 U. 1 33 2 1 5 O. 9 35 3 1 5 O. 1 3B 3 1 5 0.9 37 In comparison the slope of the spectrophotometric curve c of thechromium-cobaltous titanium oxide series pigment having a compositionsimilar to that of a or b but containing no antimony trioxide addition,has a low reflectance value of about 7% at about 670 millimicrons and ahigh reflectance value of about 37% at 750 millimicrons or an increase(AR) in precent reflectance value of about 30 units within the criticalwave length range of 670 to 7 50 millimicrons.

Example 1 5 mols titanium dioxide 3 mols chromium oxide 3 mols cobaltousoxide 1 mol antimony trioxide To test the paint making properties of thepigment material, a camouflage paint was made using this green pigmentmaterial mixed with an alkyd vehicle at 2% PVC with 11% of a calciumcarbonate extender. The paint was milled in a three roller paint milland compared with a paint prepared in the same manner but using astandard chrome green pigment. It was noted that the hiding power of thecamouflage paint of this invention was as good and in some instancesbetter than standard chrome green pigment and that its rise inreflectance value in the critical wave length range of from 67 0 to 750millimicrons was substantially identical to that of chlorophyll.

Example 11 To 2305 parts of a 27% solids hydrous titanium oxide as thesource of titanium dioxide was added parts cobalt carbonate as thesource of cobaltous oxide, 466 parts of chromium sesquioxide and 45parts antimony trioxide. The ingredients were then vigorously agitatedto insure an intimate mixture whereupon the slurry was dried andcalcined in the manner described in the foregoing example. The calcinedproduct was a soft dark green pigment which upon analysis wasfound tocomprise the following constituents on a weight basis:

5 mols titanium dioxide 2 mols chromium oxide 1 mol cobaltous oxide 0.1mol antimony trioxide When made up into a camouflage paint, this pigmentcomposition formed a paint having hiding power superior to that ofchrome green paint and an excellent rise in reflectance value within thecritical wave length range.

From the foregoing description of the invention, it will be evident thata green pigment composition comprising the cobaltous-chromium-titaniumdioxide system admixed with antimony trioxide has a spectrophotometriccurve, the percent reflectance value of which is somewhat higer thanthat of chlorophyll and is characterized by a rapid increase inreflectance units within the critical wave length range between 670 and750 millimicrons corresponding favorably with that of chlorophyll.Consequently, this pigment composition is ideally suited for use in theformation of camouflage coating compositions which cannot be detectedvisually nor by means of infra-red ray photography; and which havinghigh hiding power, low oil absorption and good resistance to weathering.

It will be understood that the examples shown are given merely for thepurpose of illustration and that other variations and embodiments may beconsidered to fall within the scope of the invention as defined by theappended claim.

I claim:

A green pigment for use in forming camouflage coating compositions whichconsists of a physico-chemical combination of chromium sesquioxide,cobaltous oxide, antimony trioxide and titanium dioxide, the amounts ofsaid oxides being analytically present, on a weight basis from:

0.5 to 5 mols chromium sesquioxide 0.5 to 5 mols cobaltous oxide 5 to 5mols titanium dioxide 0.1 to 2.7 mols antimony trioxide provided saidchromium sesquioxide is present in amounts at least equal, on a weightbasis, to the amount of cobaltous oxide, and provided further that theamount of antimony trioxide does not exceed substantially one-half theamount of cobaltous oxide when said cobaltous oxide and chromiumsesquioxide are in substantially equimolar ratios.

References Cited in the file of this patent UNITED STATES PATENTS1,891,210 Wolff Dec. 13, 1932 1,945,809 Harbert Feb. 6, 1934 2,213,168Monk et a1 Aug. 27, 1940

0.5 TO 5 MOLS CHROMIUM SESQUIOXIDE 0.5 TO 5 MOLS COBALTOUS OXIDE 5 TO 5MOLS TITANIUM DIOXIDE 0.1 TO 2.7 MOLS ANTIMONY TRIOXIDE